Studies are being performed on three parasitic parasites: Schistosomes, Giardia, and Cryptosporidium. Antibody responses in acute and chronic schistosomiasis have been compared using Western blots. Major differences between these two groups were noted and antibody responses to some antigens are predominately seen in acute or early infections. The surface antigens of Giardia and human antibody responses to Giardia antigens were compared using a variety of isolates. Studies indicate major differences in the surface antigens of Giardia isolates and the humoral reponses of man are sometimes specific to the homologous isolate. Studies of Cryptosporidium have just begun with the aim of developing a measure of antibody responses and assays for specific parasite antigen in stool.